It is the purpose of this project to delineate, at the cellular and molecular level, the mechanism of action of microbial components in immunopotentiation. In the past year, four major efforts have been made: 1) elucidating the nature of biological responses to treatment of tumors with mycobacterial cell wall derivatives combined with endotoxic extracts obtained from Salmonella typhimurium, 2) investigating the minimal structural requirements of cell wall derivatives responsible for their antitumor activity when combined with endotoxic extracts, 3) quantitative determination of the molecular interaction of these microbial substances with each other and with oil droplets of oil-in-water emulsions used as therapeutic vehicles, and 4) determining the nature of interaction of radiolabeled endotoxin with tumor cells, in vitro, by quantitative binding studies and electron microscopic autoradiography.